Sternomastoid muscle function and fatigue in breathless patients with severe respiratory disease

Ventilatory failure, ventilator support, and ventilator weaning

The development of acute ventilatory failure represents an inability of the respiratory control system to maintain a level of respiratory motor output to cope with the metabolic demands of the body. The level of respiratory motor output is also the main determinant of the degree of respiratory distress experienced by such patients. As ventilatory failure progresses and patient distress increases, mechanical ventilation is instituted to help the respiratory muscles cope with the heightened workload. While a patient is connected to a ventilator, a physician's ability to align the rhythm of the machine with the rhythm of the patient's respiratory centers becomes the primary determinant of the level of rest accorded to the respiratory muscles. Problems of alignment are manifested as failure to trigger, double triggering, an inflationary gas-flow that fails to match inspiratory demands, and an inflation phase that persists after a patient's respiratory centers have switched to expiration. With recovery from disorders that precipitated the initial bout of acute ventilatory failure, attempts are made to discontinue the ventilator (weaning). About 20% of weaning attempts fail, ultimately, because the respiratory controller is unable to sustain ventilation and this failure is signaled by development of rapid shallow breathing. Substantial advances in the medical management of acute ventilatory failure that requires ventilator assistance are most likely to result from research yielding novel insights into the operation of the respiratory control system.

Role of the respiratory muscles in acute respiratory failure of COPD: lessons from weaning failure

It is problematic to withhold therapy in a patient with chronic obstructive pulmonary disease (COPD) who presents with acute respiratory failure so that detailed physiological measurements can be obtained. Accordingly, most information on respiratory muscle activity in patients experiencing acute respiratory failure has been acquired by studying patients who fail a trial of weaning after a period of mechanical ventilation. Such patients experience marked increases in inspiratory muscle load consequent to increases in resistance, elastance, and intrinsic positive end-expiratory pressure. Inspiratory muscle strength is reduced secondary to hyperinflation and possibly direct muscle damage and the release of inflammatory mediators. Most patients recruit both their sternomastoid and expiratory muscles, even though airflow limitation prevents the expiratory muscles from lowering lung volume. Even when acute hypercapnia is present, patients do not exhibit respiratory center depression; indeed, voluntary activation of the diaphragm, in absolute terms, is greater in hypercapnic patients than in normocapnic patients. Instead, the major mechanism of acute hypercapnia is the development of rapid shallow breathing. Despite the marked increase in mechanical load and decreased force-generating capacity of the inspiratory muscles, patients do not develop long-lasting muscle fatigue, at least over the period of a failed weaning trial. Although the disease originates within the lung parenchyma, much of the distress faced by patients with COPD, especially during acute respiratory failure, is caused by the burdens imposed on the respiratory muscles.

Sternomastoid, rib cage, and expiratory muscle activity during weaning failure

We hypothesized that patients who fail weaning from mechanical ventilation recruit their inspiratory rib cage muscles sooner than they recruit their expiratory muscles, and that rib cage muscle recruitment is accompanied by recruitment of sternomastoid muscles. Accordingly, we measured sternomastoid electrical activity and changes in esophageal (ΔPes) and gastric pressure (ΔPga) in 11 weaning-failure and 8 weaning-success patients. At the start of trial, failure patients exhibited a higher ΔPga-to-ΔPes ratio than did success patients ( P = 0.05), whereas expiratory rise in Pga was equivalent in the two groups. Between the start and end of the trial, failure patients developed additional increases in ΔPga-to-ΔPes ratio ( P < 0.0014) and the expiratory rise in Pga also increased ( P < 0.004). At the start of trial, sternomastoid activity was present in 8 of 11 failure patients contrasted with 1 of 8 success patients. Over the course of the trial, sternomastoid activity increased by 53.0 ± 9.3% in the failure patients ( P = 0.0005), whereas it did not change in the success patients. Failure patients recruited their respiratory muscles in a sequential manner. The sequence began with activity of diaphragm and greater-than-normal activity of inspiratory rib cage muscles; recruitment of sternomastoids and rib cage muscles approached near maximum within 4 min of trial commencement; expiratory muscles were recruited slowest of all. In conclusion, not only is activity of the inspiratory rib cage muscles increased during a failed weaning trial, but respiratory centers also recruit sternomastoid and expiratory muscles. Extradiaphragmatic muscle recruitment may be a mechanism for offsetting the effects of increased load on a weak diaphragm.

Mechanics of Respiratory Muscles in Single-Lung Transplant Recipients

BACKGROUND

Emphysema and pulmonary fibrosis force the patients to breathe at an abnormal lung volume, which alters the lengths of the respiratory muscles and thereby their work capability is reduced. After single-lung transplantation, muscle function is restored on the side of the transplant but it may be asymmetric to that on the side of the native diseased lung.

OBJECTIVE

Investigating the hypothesis that single-lung transplantation induces mechanical asymmetry of the respiratory muscles on the two sides.

METHODS

Simultaneously noninvasive measurements of inspiratory and expiratory mouth pressure, airflow rate and electromyography signals from the sternomastoid, external intercostal, rectus abdominis and external oblique muscles were acquired during different breathing maneuvers. The study group included 10 single-lung transplant recipients (5 with pulmonary fibrosis and 5 with emphysema) and 10 healthy controls.

RESULTS

Analysis of the finding shows a significant lower global strength of the respiratory muscles of single-lung transplant recipients compared to that of healthy subjects. No significant difference in the EMG signals of respiratory muscles was found either between the different groups or between the sides of the transplant and the native lung in the patient groups. Both single-lung transplant recipients and healthy subjects demonstrated high EMG activity of the inspiratory muscles during inspiration at different breathing efforts.

CONCLUSION

Patients after single-lung transplantation have lower respiratory muscle strength than healthy subjects, but apparently normal electrical activity. The lower global respiratory muscle strength emphasizes the importance of their rehabilitation before and after single-lung transplantation.

Breathing pattern and carbon dioxide retention in severe chronic obstructive pulmonary disease

BACKGROUND

The factors leading to chronic hypercapnia and rapid shallow breathing in patients with severe chronic obstructive pulmonary disease (COPD) are not completely understood. In this study the interrelations between chronic carbon dioxide retention, breathing pattern, dyspnoea, and the pressure required for breathing relative to inspiratory muscle strength in stable COPD patients with severe airflow obstruction were studied.

METHODS

Thirty patients with COPD in a clinically stable condition with forced expiratory volume in one second (FEV1) of < 1 litre were studied. In each patient the following parameters were assessed: (1) dyspnoea scale rating, (2) inspiratory muscle strength by measuring minimal pleural pressure (PPLmin), and (3) tidal volume (VT), flow, pleural pressure swing (PPLsw), total lung resistance (RL), dynamic lung elastance (ELdyn), and positive end expiratory alveolar pressure (PEEPi) during resting breathing.

RESULTS

Arterial carbon dioxide tension (PaCO2) related directly to RL/PPLmin, and ELdyn/PPLmin, and inversely to VT and PPLmin. There was no relationship between PaCO2 and functional residual capacity (FRC), total lung capacity (TLC), or minute ventilation. PEEPi was similar in eucapnic and hypercapnic patients. Expressing PaCO2 as a combined function of VT and PPLmin (stepwise multiple regression analysis) explained 71% of the variance in PaCO2. Tidal volume was directly related to inspiratory time (TI), and TI was inversely related to the pressure required for breathing relative to inspiratory muscle strength (PPLsw, %PPLmin). There was an association between the severity of dyspnoea and both the increase in PPLsw (%PPLmin) and the shortening in TI.

CONCLUSIONS

The results indicate that, in stable patients with COPD with severe airflow obstruction, hypercapnia is associated with shallow breathing and inspiratory muscle weakness, and rapid and shallow breathing appears to be linked to both a marked increase in the pressure required for breathing relative to inspiratory muscle strength and to the severity of the breathlessness.

Validation of creatine, glycogen and L-(+)-lactate determination in biopsy samples of bovine Musculus diaphragma

Whereas reliable measurements of diaphragmatic force and electrical activity are now available in calves, evidence that substrate contents in the bovine diaphragm can be accurately measured is still lacking. The purposes of the present study were therefore a) to describe and test the reliability of methods and procedures used for sampling, lyophilisation, extraction and dosage of muscular lactate, glycogen and creatine contents and b) to report the variation in their levels found along the bovine diaphragm and among individuals. The repeatability of the results yielded by a) assaying the extracts, b) processing and assaying the extracts and c) taking samples at different sites in the muscle was assessed. Neither assay, nor processing effects were significant (P < or = 0.05). Substrates were found to be homogeneously distributed within the two muscles studied. Substrate contents expressed per unit of muscle weight or total creatine were neither more or less variable than when expressed per unit of dry matter.

Respiratory muscles and ventilatory failure: 1993 perspective

Some conditions that predispose to ventilatory failure increase the work of breathing (chronic obstructive pulmonary disease [COPD], obesity, kyphoscoliosis), whereas others cause severe respiratory muscle weakness. Specific reasons for muscle weakness include critical illness (electrolyte imbalance, acidemia, shock, sepsis), chronic illness (poor nutrition, cachexia), and neuromuscular diseases. Inspiratory muscle weakness from mechanical disadvantage to the diaphragm is characteristic of asthma and COPD. The increased work of breathing combined with muscle weakness increases the pressure needed to inspire a breath and decreases maximal inspiratory pressure. When this pressure exceeds 0.4, dyspnea and inspiratory muscle fatigue ensue. One way to lower this pressure and avert fatigue is to lower the tidal volume. Ventilatory drive is high, not low, in ventilatory failure. Concomitant shortening of inspiration and breath duration cause the small tidal volume and increased respiratory rate. Gas exchange is compromised by ventilation/perfusion imbalance, and the ratio of dead space to tidal volume is also increased by rapid, shallow breathing. Reduction in tidal volume minimizes dyspnea, but the small tidal volume is inadequate for gas exchange. Acute treatment of respiratory muscle failure involves respiratory muscle rest through mechanical ventilation and removal of noxious influences (infection, metabolic disarray), whereas chronic treatment involves rebuilding the contractile apparatus by nutritional repletion and training.

Rehabilitation of spinal cord injured patients on long term ventilation

Recent advances in roadside management and resuscitation techniques have resulted in an increased survival rate of people with high cervical cord injury. A few become partially or permanently ventilator dependent. Not only are these people dependent on assisted ventilation, but their speech is also compromised, along with loss of voluntary control and many other bodily functions, as they are tetraplegic. By using recent technological advancements, such as portable ventilators, phrenic nerve stimulation, environmental controls and specialised wheelchairs it has been possible to manage such patients at home. Furthermore, patients on ventilators are unable to have verbal communication. There is therefore a need for them to develop either augmentative communication or the use of alternative communication aids. Recent published reports indicate the factors other than the clinical state that may prevent such patients from taking advantage of modern advances; the main issues appear to be cost factors, community care provision and ethical considerations.

Detection and severity of low frequency fatigue in the human adductor pollicis muscle

The sensitivity of electrical stimulation tests for detecting low frequency fatigue (LFF) and its duration were examined in the adductor pollicis muscle of ten normal subjects. Supramaximal stimulation was applied to the ulnar nerve at the wrist and values for test stimulation force ratios of 10:100 Hz, 15:100 Hz and 20:50 Hz (2 sec at each frequency with 5 min rest between each ratio) were obtained for fresh muscle. Fatigue was then induced by voluntary isometric contractions at 50% maximal voluntary force (MVC) repeated until only 30% MVC could be achieved. Contractions lasted 10 sec with 5 sec rest between each. The three test ratios were then repeated to monitor recovery at intervals up to 72 h after activity. High frequency forces returned to fresh values by 24 h but low frequency forces were all still significantly reduced. Forces at 10 and 15 Hz were still significantly reduced at 48 and 72 h (10 Hz greater than fatigue than 15 Hz). The low/high frequency ratios, calculated once 50 and 100 Hz forces had recovered, also demonstrated differences in recovery rates. Repeatability tests indicated that 10 Hz force was more variable than other frequencies and forces at all stimulation frequencies were repeatable on different days with a coefficient of variation of less than 15%. Values for the 15:100 Hz ratio from fresh muscle in 22 normal subjects were 0.48 +/- 8. The 15:100 Hz ratio is suggested as the most appropriate test ratio for detecting LFF since 15 Hz force is more sensitive than 20 Hz and more stable than 10 Hz.

Dyspnea-limited response in chronic obstructive pulmonary disease: reduced unsupported arm activities

Dyspnea, the sensation of uncomfortable breathing, is the primary activity-limiting symptom leading to reduced functional ability in chronic obstructive pulmonary disease (COPD). Patients with severe COPD report a marked increase in the sensation of dyspnea with routine tasks that require arm use, especially activities necessitating unsupported arm elevation. Dyspnea is associated with alterations in respiratory muscle function, such as an increase in muscle force requirement, a reduction in respiratory muscle strength and endurance, and an increase in the recruitment of the rib cage and accessory muscles. Unsupported arm exercise (UAE) further compromises respiratory muscle capacity for ventilation because it requires the muscles' concomitant recruitment in the maintenance of chest wall stabilization. This article presents respiratory muscle mechanisms leading to reduced UAE, methods of measuring unsupported arm endurance, and treatment strategies to improve unsupported arm activity endurance in patients with COPD.

The pattern of respiratory muscle recruitment during pursed-lip breathing

Data from the present study indicate a change in the pattern of chest wall muscle recruitment and improved ventilation with pursed-lip breathing (PLB) in COPD. Pursed lip breathing led to increased rib cage and accessory muscle recruitment during inspiration and expiration, increased abdominal muscle recruitment during expiration, decreased duty cycle of the inspiratory muscles and respiratory rate, and improved SaO2. In addition, PLB resulted in no change in pressure across the diaphragm and a less fatiguing breathing pattern of the diaphragm. Changes in chest wall muscle recruitment and respiratory temporal parameters concomitant with the increased SaO2 indicate a mechanism of improving ventilation with PLB while protecting the diaphragm from fatigue in COPD. Alterations in the pattern of respiratory muscle recruitment with PLB may be associated also with the amelioration of dyspnea. Further investigation is necessary to explore the relationship between the pattern of respiratory muscle recruitment during PLB and dyspnea.

Reversible T-wave abnormality in severe acute asthma: an electrocardiographic sign of severity

Reversible electrocardiographic (ECG) abnormalities are well recognized in severe acute asthma. Inferior lead T-wave abnormalities have only rarely been reported, and their frequency and significance have not been well documented. We studied 70 consecutive patients with severe acute asthma on admission to hospital and during recovery, in order to examine the frequency and natural history of such changes and to document their relationship to the severity of the attack. Twenty-two patients (34%) had inferior lead T-wave inversion on ECGs performed within 1 h of admission (group 1), whereas the rest did not (group 2). Apart from sinus tachycardia this was the most common ECG abnormality. Patients with inferior T-wave inversion were found to have more severe asthma in terms of degree of pulsus paradoxus, peak expiratory flow rate, forced expiratory volume in 1 s and arterial blood oxygen tension. Ten group 1 and ten group 2 patients underwent two-dimensional echocardiography during the acute phase of their illness and during recovery. Six (60%) group 1 patients showed echocardiographic evidence of right ventricular pressure overload compared with only one (10%) patient in group 2 (P less than 0.02). Following recovery, voluntary hyperventilation and exercise testing in ten group 1 patients failed to reproduce the ECG changes seen on admission. Reversible inferior lead T-wave abnormalities may occur in the severe acute asthma and appear to be related to the severity of the attack.

Dyspnea: a case for nursing diagnosis status

Dyspnea, the unpleasant subjective sensation of difficult breathing, is one of the most common symptoms experienced by patients with pulmonary and cardiac disorders. This article reviews the research concerning dyspnea and proposes it for consideration as a nursing diagnosis. The etiologies are categorized according to the neurosensory, neurochemical, cognitive, and affective mechanisms. The defining characteristics include the subjective words describing dyspnea, such as shortness of breath, suffocation, and tightness. The most supported objective sign of dyspnea in the literature is an increased use of accessory muscles of respiration. Nursing interventions for dyspnea relief are geared toward reducing the afferent activity from receptors in the respiratory muscles and dealing with the affective component of dyspnea. These interventions include pacing activities, breathing techniques, and inducing the relaxation response. Because most research for interventions to reduce dyspnea have focused on patients with obstructive lung disorders who have chronic dyspnea, recommendations for further research include using acutely ill patients and those with a variety of medical conditions.

Respiratory response to arm elevation in patients with chronic airflow obstruction

We have shown that patients with chronic airflow obstruction (CAO) complain of disabling dyspnea when performing seemingly trivial tasks with unsupported arms. Surprisingly little is known about the metabolic and ventilatory responses to unsupported upper extremity activity even though some of the muscles of the upper torso and shoulder girdle are used to perform simple and complex everyday tasks as well as partake in ventilation. To determine the effect of simple arm elevation in 20 patients with CAO we studied their lung function, VO2, VCO2, and VE, with arms down at the side (AD), during 2 min with arms extended forward up to shoulder level (AE), and during recovery. To determine the pattern of ventilatory muscle recruitment we also measured endoesophageal (Ppl), gastric (Pg), and transdiaphragmatic (Pdl) pressures. In five of the patients the electromyographic signal (EMG) of the sternocleidomastoid (Sm) muscle was recorded and analyzed in its time domain (amplitude) and power spectrum density (median frequency). Within 30 s of arm elevation VO2, VCO2, and VE rose and remained elevated for 1 min after the arms were lowered. The increase in VE resulted from increases in respiratory rate and minimal rise in tidal volume (VT). With AE, FEV1 decreased by 5% (p less than 0.02) but FRC increased by 2% (p less than 0.05). Peak inspiratory pressure (Pimax) dropped from 54 +/- 4 to 48 +/- 4 cm H2O (p less than 0.005); Pdimax remained unchanged. Immediately after raising the arms Pgi, inspiratory swing in Pdi (delta Pdi), end-expiratory Ppl, and end-expiratory Pg increased significantly.(ABSTRACT TRUNCATED AT 250 WORDS)

Muscle fatigue in acute respiratory failure

Fatigue of the respiratory muscles is now well documented but still remains a process that cannot be assessed easily. Several methods are available to detect fatigue; they represent windows allowing different viewpoints on the same phenomenon. The definition and determinants of respiratory muscle fatigue and some of the methods used to detect it are reviewed. On the basis of the available evidence provided by each of these methods, the role played by muscle fatigue in acute respiratory failure (ARF) is discussed.

Effect of low frequency fatigue on human muscle strength and fatigability during subsequent stimulated activity

Fatiguing contractions of the adductor pollicis muscle were produced by intermittent supramaximal stimulation of the ulnar nerve in a set frequency pattern, in six normal subjects. At the end of an initial fatiguing contraction series, low frequency fatigue (LFF) had been induced and persisted at 15 min of recovery. Stimulated fatiguing activity was then repeated in an identical fashion to the initial series. At high frequencies, declines in force were similar for both series. At low frequencies, declines in force were greater during the second series despite similar changes in compound muscle action potential amplitude. This confirmation that LFF persists during subsequent stimulated activity, and reduces low but not high frequency fatigue resistance, suggests that the impaired endurance of fatigued muscle during voluntary activity primarily results from peripheral changes at low frequency. These findings also have implications for therapeutic electrical stimulation of muscle.